Hans Suess and climate change

Suess effect

The Suess effect is a change in the ratio of the atmospheric concentrations of heavy isotopes of carbon (13C and 14C) by the admixture of large amounts of fossil-fuel derived CO2, which is depleted in 13CO2 and contains no 14CO2. It is named for the Austrian chemist Hans Suess, who noted the influence of this effect on the accuracy of radiocarbon dating. More recently, the Suess effect has been used in studies of climate change. The term originally referred only to dilution of atmospheric 14CO2. The concept was later extended to dilution of 13CO2 and to other reservoirs of carbon such as the oceans and soils.

Carbon isotopes

Carbon has three naturally occurring isotopes. About 99% of carbon on Earth is carbon-12 (12C), about 1% is carbon-13 (13C), and a trace amount is carbon-14 (14C). The 12C and 13C isotopes are stable, while 14C decays radioactively to nitrogen-14 (14N) with a half life of 5730 years. 14C on Earth is produced nearly exclusively by the interaction of cosmic radiation with the upper atmosphere. A 14C atom is created when a thermal neutron displaces a proton in 14N. Minuscule amounts of 14C are produced by other radioactive processes, and a significant amount was released into the atmosphere during nuclear testing before the Limited Test Ban Treaty. Natural 14C production and hence atmospheric concentration varies only slightly over time.

Plants take up 14C by fixing atmospheric carbon through photosynthesis. Animals then take 14C into their bodies when they consume plants (or consume other animals that consume plants). Thus, living plants and animals have the same ratio of 14C to 12C as the atmospheric CO2. Once organisms die they stop exchanging carbon with the atmosphere, and thus no longer take up new 14C. Radioactive decay then gradually depletes the 14C in the organism. This effect is the basis of radiocarbon dating.

Photosynthetically fixed carbon in terrestrial plants is depleted in 13C compared to atmospheric CO2. This depletion is slight in C4 plants but much greater in C3 plants which form the bulk of terrestrial biomass worldwide. Depletion in CAM plants vary between the values observed for C3 and C4 plants. In addition, most fossil fuels originate from C3 biological material produced tens to hundreds of millions of years ago. C4 plants did not become common until about 6 to 8 million years ago, and although CAM photosynthesis is present in modern relatives of the Lepidodendrales of the Carboniferous lowland forests, even if these plants also had CAM photosynthesis they were not a major component of the total biomass.

Fossil fuels such as coal and oil are made primarily of plant material that was deposited millions of years ago. This period of time equates to thousands of half-lives of 14C, so essentially all of the 14C in fossil fuels has decayed. Fossil fuels also are depleted in 13C relative to the atmosphere, because they were originally formed from living organisms. Therefore, the carbon from fossil fuels that is returned to the atmosphere through combustion is depleted in both 13C and 14C compared to atmospheric carbon dioxide.

 

 

 

Spectral properties of Proxima

The full spectral radiative properties of Proxima Centauri

ABSTRACT: The discovery of Proxima b, a terrestrial temperate planet, presents the opportunity of studying a potentially habitable world in optimal conditions. A key aspect to model its habitability is to understand the radiation environment of the planet in the full spectral domain. We characterize the X-rays to mid-IR radiative properties of Proxima with the goal of providing the top-of-atmosphere fluxes on the planet. We also aim at constraining the fundamental properties of the star. We employ observations from a large number of facilities and make use of different methodologies to piece together the full spectral energy distribution of Proxima. In the high-energy domain, we pay particular attention to the contribution by rotational modulation, activity cycle, and flares so that the data provided are representative of the overall radiation dose received by the atmosphere of the planet. We present the full spectrum of Proxima covering 0.7 to 30000 nm. The integration of the data shows that the top-of-atmosphere average XUV irradiance on Proxima b is 0.293 W m-2, i.e., nearly 60 times higher than Earth, and that the total irradiance is 877±44 W m-2, or 64±3% of the solar constant but with a significantly redder spectrum. We also provide laws for the XUV evolution of Proxima corresponding to two scenarios. Regarding the fundamental properties of Proxima, we find M=0.120±0.003 Msun, R=0.146±0.007 Rsun, Teff=2980±80 K, and L=0.00151±0.00008 Lsun. In addition, our analysis reveals a ~20% excess in the 3-30 micron flux of the star that is best interpreted as arising from warm dust in the system. The data provided here should be useful to further investigate the current atmospheric properties of Proxima b as well as its past history, with the overall aim of firmly establishing the habitability of the planet.

 

Meteorer målt med infralyd

Refinement of Bolide Characteristics from Infrasound measurements

ABSTRACT: We have detected and performed signal measurements on 78 individual bolide events as recorded at 179 infrasound stations between 2006 and 2015. We compared period-yield relations with AFTAC nuclear period-yield data, finding these to be similar with a slight offset. Scatter in period measurements for individual bolide is found to be caused in part by station noise levels and by attenuation effects with range. No correlation was found between the infrasound signal period and any of bolide height at peak brightness, entry speed or impact angle. We examined in detail three well constrained bolides having energy deposition curves, known trajectories and infrasound detections finding some evidence at shorter ranges that a component of station period scatter is due to varying source heights sampled by different stations. However, for longer-range stations in these three case studies, we were not able to assign unique source heights using raytracing due to large uncertainties in atmospheric conditions. Our results suggest that while source height contributes to the observed variance in infrasound signal periods from a given bolide, range and station noise play a larger role.

 

Hvordan blev kometerne dannet?

How Were the Comets Made?

Explaining the composition of these 4.5 billion-year-old relics may require scientists to revise their models of the primitive solar nebula.

Joseph A. Nuth III

Every once in a while a dirty snowball—in the form of a comet—swoops through the night sky from the outer reaches of our solar system. Though a comet is beautiful to behold, the sudden appearance of these celestial interlopers has a long history of terrifying our ancestors and, more recently, of worrying the modern public about doomsday-impact threats. To the astronomer, however, comets are a puzzle that must be solved. They contain crystalline dust grains that could only have formed at very high temperatures, yet they also contain ices that simply could not have survived the heat needed to make the crystals. How did the hot and cold parts come together to form the flying amalgam we call a comet? It turns out that the answer to the puzzle may require astronomers to revise their models of how our solar system formed.

In general, we believe that comets begin to form by an accreting “snowball” effect in which the icy dust grains stick together to form fractal-like aggregates. This process begins at some considerable distance from the center of the solar nebula, perhaps as far as 100 astronomical units (AU) away. (For a sense of scale, consider that the Earth is merely one AU from the Sun, whereas Pluto is 40 AU away.) At this stage, the movements of the dust grains and the small aggregates are coupled to the movements of the ambient nebular gas. Over time, however, as the aggregates accumulate into compact, boulder-sized snowballs, or cometesimals, they are slowed down by drag in the ambient gas, and they start to drift inward as their orbits decay. As the cometesimals fall closer to the center of the solar nebula, they continue to grow by the accretion of ice and dust grains, as well as by merging with other aggregates in their path. In due course this pile of rubble becomes a comet, perhaps 10 to 20 kilometers across, which contains a collection of materials from a wide swath of its orbital radius.

Scientists who study meteorites have known for decades that a certain amount of mixing must have taken place in the primitive solar nebula. Some meteorites contain highly processed materials that are inexplicably embedded within a matrix of very primitive materials. The processed materials include the CAIs (calcium-aluminum inclusions), which required temperatures peaking near 2,200 kelvins for their manufacture, and the chondrules, which contain less heat-resistant minerals (such as olivine and plagioclase) that saw temperatures no higher than 1,700 kelvins. The CAIs and the chondrules are often embedded in a matrix containing highly fragile carbon-based components (diamond, graphite and silicon carbide grains), some of which are only a few nanometers across, and would be destroyed at temperatures as low as 600 kelvins.

Pieces of the puzzle began to come together in the mid-1990s when astronomers studying a superficially unrelated problem came up with a viable mechanism for mixing materials in the solar nebula. Frank Shu and his colleagues at the University of California, Berkeley, were trying to understand the dynamic interactions between growing protostars and their nebular accretion disks. According to their calculations, interactions between the disk and the protostar could produce a powerful wind that could account for the bipolar outflows observed around many young stars. Soon after proposing this “extraordinary wind” (or X-wind) model, Shu’s team realized that the same violent interactions might be responsible for producing both the CAIs and the chondrules in the solar nebula. The interface between the surface of the protostar and the inner edge of the accretion disk was just the right temperature to produce these meteoritic inclusions. Moreover, these winds could then toss the finished products out to about 3 to 10 AU, where they would be incorporated into accreting planetesimals and become part of some planet or asteroid.

Although the X-wind model does well in explaining the composition of meteorites, it does not provide an easy mechanism for annealing amorphous silicates to produce the crystalline grains seen in comets. Individual grains exposed to the 1,600- to 2,200-kelvin temperatures of the X-wind near the inner edge of the accretion disk would be vaporized rather than crystallized. When the vapors later cooled and recondensed, it is likely that they would form amorphous silicates (such as those observed in circumstellar outflows around other stars), rather than the crystalline grains seen in comets.

All of this suggests that the theoreticians need to add yet another level of complexity to the dynamic models of the solar nebula. There must be a mechanism that is capable of transporting grains that have been annealed at temperatures near 1,000 kelvins, out to regions where the ices of water and hydrocarbons are stable and the cometesimals begin to accrete. One possibility is the presence of large-scale convective cells near the inner regions of the disk that interact with material in the X-wind in such a way that some of the dust and gas becomes entrained and transported outward.

Winds in the solar nebula may have been responsible for the mixing of “hot” and “cold” components found in both meteorites and comets. Meteorites contain calcium-aluminum-rich inclusions (CAIs, formed at about 2,000 kelvins) and chondrules (formed at about 1,650 kelvins), which were created near the protosun and then blown (green arrows) several astronomical units away, into the region of the asteroids between Mars and Jupiter, where they were embedded in a matrix of temperature-sensitive, carbon-based “cold” components. The “hot” component in comets tiny grains of annealed silicate dust (olivine) is vaporized at about 1,600 kelvins, suggesting that it never reached the innermost region of the disk before it was transported (white arrows) out beyond the orbit of Pluto, where it was mixed with ices and unheated silicate dust (“cold” components). Vigorous convection in the accretion disk may have contributed to the transport of materials. This scenario is based on the X-wind model of the solar nebula developed by Frank Shu and his colleagues at the University of California, Berkeley.

 

 

Properties of Taurid meteoroids

Spectra and physical properties of Taurid meteoroids

ABSTRACT: Taurids are an extensive stream of particles produced by comet 2P/Encke, which can be observed mainly in October and November as a series of meteor showers rich in bright fireballs. Several near-Earth asteroids have also been linked with the meteoroid complex, and recently the orbits of two carbonaceous meteorites were proposed to be related to the stream, raising interesting questions about the origin of the complex and the composition of 2P/Encke. Our aim is to investigate the nature and diversity of Taurid meteoroids by studying their spectral, orbital, and physical properties determined from video meteor observations. Here we analyze 33 Taurid meteor spectra captured during the predicted outburst in November 2015 by stations in Slovakia and Chile, including 14 multi-station observations for which the orbital elements, material strength parameters, dynamic pressures, and mineralogical densities were determined. It was found that while orbits of the 2015 Taurids show similarities with several associated asteroids, the obtained spectral and physical characteristics point towards cometary origin with highly heterogeneous content. Observed spectra exhibited large dispersion of iron content and significant Na intensity in all cases. The determined material strengths are typically cometary in the KB classification, while PE criterion is on average close to values characteristic for carbonaceous bodies. The studied meteoroids were found to break up under low dynamic pressures of 0.02 – 0.10 MPa, and were characterized by low mineralogical densities of 1.3 – 2.5 g cm-3. The widest spectral classification of Taurid meteors to date is presented.

 

Green Bank Ammonia Survey

The Green Bank Ammonia Survey (GAS): First Results of NH3 mapping the Gould Belt

ABSTRACT: We present an overview of the first data release (DR1) and first-look science from the Green Bank Ammonia Survey (GAS). GAS is a Large Program at the Green Bank Telescope to map all Gould Belt star-forming regions with AV ≳ 7 mag visible from the northern hemisphere in emission from NH3 and other key molecular tracers. This first release includes the data for four regions in Gould Belt clouds: B18 in Taurus, NGC 1333 in Perseus, L1688 in Ophiuchus, and Orion A North in Orion. We compare the NH3 emission to dust continuum emission from Herschel, and find that the two tracers correspond closely. NH3 is present in over 60% of lines-of-sight with AV ≳ 7 mag in three of the four DR1 regions, in agreement with expectations from previous observations. The sole exception is B18, where NH3 is detected toward ~ 40% of lines-of-sight with AV ≳ 7 mag. Moreover, we find that the NH3 emission is generally extended beyond the typical 0.1 pc length scales of dense cores. We produce maps of the gas kinematics, temperature, and NH3 column densities through forward modeling of the hyperfine structure of the NH3 (1,1) and (2,2) lines. We show that the NH3 velocity dispersion, σv, and gas kinetic temperature, TK, vary systematically between the regions included in this release, with an increase in both the mean value and spread of σv and TK with increasing star formation activity. The data presented in this paper are publicly available.

 

LHCb finds intriguing anomalies

LHCb finds new hints of possible Standard Model deviations

The LHCb experiment finds intriguing anomalies in the way some particles decay. If confirmed, these would be a sign of new physics phenomena not predicted by the Standard Model of particle physics. The observed signal is still of limited statistical significance, but strengthens similar indications from earlier studies. Forthcoming data and follow-up analyses will establish whether these hints are indeed cracks in the Standard Model or a statistical fluctuation.

Today, in a seminar at CERN, the LHCb collaboration presented new long-awaited results on a particular decay of B0 mesons produced in collisions at the Large Hadron Collider. The Standard Model of particle physics predicts the probability of the many possible decay modes of B0 mesons, and possible discrepancies with the data would signal new physics.

In this study, the LHCb collaboration looked at the decays of B0 mesons to an excited kaon and a pair of electrons or muons. The muon is 200 times heavier than the electron, but in the Standard Model its interactions are otherwise identical to those of the electron, a property known as lepton universality. Lepton universality predicts that, up to a small and calculable effect due to the mass difference, electron and muons should be produced with the same probability in this specific B0 decay. LHCb finds instead that the decays involving muons occur less often.

While potentially exciting, the discrepancy with the Standard Model occurs at the level of 2.2 to 2.5 sigma, which is not yet sufficient to draw a firm conclusion. However, the result is intriguing because a recent measurement by LHCb involving a related decay exhibited similar behaviour.

While of great interest, these hints are not enough to come to a conclusive statement. Although of a different nature, there have been many previous measurements supporting the symmetry between electrons and muons. More data and more observations of similar decays are needed in order to clarify whether these hints are just a statistical fluctuation or the first signs for new particles that would extend and complete the Standard Model of particles physics. The measurements discussed were obtained using the entire data sample of the first period of exploitation of the Large Hadron Collider (Run 1). If the new measurements indeed point to physics beyond the Standard Model, the larger data sample collected in Run 2 will be sufficient to confirm these effects.

 

New Z’ boson at the LHC?

Physicists detect whiff of new particle at the Large Hadron Collider

By Adrian Cho | Apr. 18, 2017 , 4:45 PM

For decades, particle physicists have yearned for physics beyond their tried-and-true standard model. Now, they are finding signs of something unexpected at the Large Hadron Collider (LHC), the world’s biggest atom smasher at CERN, the European particle physics laboratory near Geneva, Switzerland. The hints come not from the LHC’s two large detectors, which have yielded no new particles since they bagged the last missing piece of the standard model, the Higgs boson, in 2012, but from a smaller detector, called LHCb, that precisely measures the decays of familiar particles.

The latest signal involves deviations in the decays of particles called B mesons—weak evidence on its own. But together with other hints, it could point to new particles lying on the high-energy horizon. “This has never happened before, to observe a set of coherent deviations that could be explained in a very economical way with one single new physics contribution,” says Joaquim Matias, a theorist at the Autonomous University of Barcelona in Spain. Matias says the evidence is strong enough for a discovery claim, but others urge caution.

The LHC smashes protons together at unprecedented energy to try to blast into existence massive new particles, which its two big detectors, ATLAS and CMS, would spot. LHCb focuses on familiar particles, in particular B mesons, using an exquisitely sensitive tracking detector to sniff out the tiny explosive decays.

B mesons are made of fundamental particles called quarks. Familiar protons and neutrons are made of two flavors of quarks, up and down, bound in trios. Heavier quark flavors—charm, strange, top, and bottom—can be created, along with their antimatter counterparts, in high-energy particle collisions; they pair with antiquarks to form mesons.

Lasting only a thousandth of a nanosecond, B mesons potentially provide a window onto new physics. Thanks to quantum uncertainty, their interiors roil with particles that flit in and out of existence and can affect how they decay. Any new particles tickling the innards of B mesons—even ones too massive for the LHC to create—could cause the rates and details of those decays to deviate from predictions in the standard model. It’s an indirect method of hunting new particles with a proven track record. In the 1970s, when only the up, down, and strange quarks were known, physicists predicted the existence of the charm quark by discovering oddities in the decays of K mesons (a family of mesons all containing a strange quark bound to an antiquark).

In their latest result, reported today in a talk at CERN, LHCb physicists find that when one type of B meson decays into a K meson, its byproducts are skewed: The decay produces a muon (a cousin of the electron) and an antimuon less often than it makes an electron and a positron. In the standard model, those rates should be equal, says Guy Wilkinson, a physicist at the University of Oxford in the United Kingdom and spokesperson for the 770-member LHCb team. “This measurement is of particular interest because theoretically it’s very, very clean,” he says.

The result is just one of half a dozen faint clues LHCb physicists have found that all seem to jibe. For example, in 2013, they examined the angles at which particles emerge in such B meson decays and found that they didn’t quite agree with predictions.

What all those anomalies point to is less certain. Within the standard model, a B meson decays to a K meson only through a complicated “loop” process in which the bottom quark briefly turns into a top quark before becoming a strange quark. To do that, it has to emit and reabsorb a W boson, a “force particle” that conveys the weak force (see graphic, previous page).

The new data suggest the bottom quark might morph directly into a strange quark—a change the standard model forbids—by spitting out a new particle called a Z′ boson. That hypothetical cousin of the Z boson would be the first particle beyond the standard model and would add a new force to theory. The extra decay process would lower production of muons, explaining the anomaly. “It sort of an ad hoc construct, but it fits the data beautifully,” says Wolfgang Altmannshofer, a theorist at the University of Cincinnati in Ohio. Others have proposed that a quark–electron hybrid called a leptoquark might briefly materialize in the loop process and provide another way to explain the discrepancies.

Of course, the case for new physics could be a mirage of statistical fluctuations. Physicists with ATLAS and CMS 18 months ago reported hints of a hugely massive new particle only to see them fade away with more data. The current signs are about as strong as those were, Altmannshofer says.

The fact that physicists are using LHCb to search in the weeds for signs of something new underscores the fact that the LHC hasn’t yet lived up to its promise. “ATLAS and CMS were the detectors that were going to discover new things, and LHCb was going to be more complementary,” Matias says. “But things go as they go.”

If the Z′ or leptoquarks exist, then the LHC might have a chance to blast them into bona fide, albeit fleeting, existence, Matias says. The LHC is now revving up after its winter shutdown. Next month, the particle hunters will return to their quest.

 

The O2 A-band in exoplanets

The O2 A-band in fluxes and polarization of starlight reflected by Earth-like exoplanets

ABSTRACT: Earth-like, potentially habitable exoplanets are prime targets in the search for extraterrestrial life. Information about their atmosphere and surface can be derived by analyzing light of the parent star reflected by the planet. We investigate the influence of the surface albedo As, the optical thickness bcloud and altitude of water clouds, and the mixing ratio η of biosignature O2 on the strength of the O2 A-band (around 760 nm) in flux and polarization spectra of starlight reflected by Earth-like exoplanets. Our computations for horizontally homogeneous planets show that small mixing ratios (η < 0.4) will yield moderately deep bands in flux and moderate to small band strengths in polarization, and that clouds will usually decrease the band depth in flux and the band strength in polarization. However, cloud influence will be strongly dependent on their properties such as optical thickness, top altitude, particle phase, coverage fraction, horizontal distribution. Depending on the surface albedo, and cloud properties, different O2 mixing ratios η can give similar absorption band depths in flux and band strengths in polarization, in particular if the clouds have moderate to high optical thicknesses. Measuring both the flux and the polarization is essential to reduce the degeneracies, although it will not solve them, in particular not for horizontally inhomogeneous planets. Observations at a wide range of phase angles and with a high temporal resolution could help to derive cloud properties and, once those are known, the mixing ratio of O2 or any other absorbing gas.

Moist Upper Atmospheres

NIR-Driven Moist Upper Atmospheres of Synchronously Rotating Temperate Terrestrial Exoplanets

ABSTRACT: H2O is a key molecule in characterizing atmospheres of temperate terrestrial planets, and observations of transmission spectra are expected to play a primary role in detecting its signatures in the near future. Detectability of H2O absorption features in transmission spectra depends on the abundance of water vapor in the upper part of the atmosphere. While the stratospheric water vapor mixing ratio of the Earth is less than 10-5 due to the cold trap, the efficiency of the cold trap depends on atmospheric properties. Here we study the 3D distribution of atmospheric H2O for synchronously rotating Earth-sized aquaplanets using the GCM ROCKE-3D, and examine the effects of total incident flux and stellar spectral type. We observe a more gentle increase of the water vapor mixing ratio in response to increased incident flux than 1D models suggest, in qualitative agreement with the climate-stabilizing effect of clouds around the substellar point previously observed in GCMs applied to synchronously rotating planets. However, the water vapor mixing ratio in the upper atmosphere starts to increase while the surface temperature is still moderate. This is explained by the circulation in the upper atmosphere driven by the radiative heating due to absorption by water vapor and cloud particles, causing efficient vertical transport of water vapor. Consistently, the water vapor mixing ratio is found to be well correlated with the near-infrared portion of the incident flux. Our results imply that various levels of water vapor mixing ratio in the upper atmosphere may be expected for synchronously rotating temperate terrestrial planets, and that for the more highly irradiated ones the H2O absorption features in the transmission spectra are strengthened by a factor of a few, loosening the observational demands for a direct H2O detection.